Quadrupole mass filters are often employed as a component of a triple stage mass spectrometry system. By way of non-limiting example, FIG. 1A schematically illustrates a triple-quadrupole system, as generally designated by the reference numeral 1. The operation of mass spectrometer 1 can be controlled and data 68 can be acquired by a control and data system (not depicted) of various circuitry of one or more known types, which may be implemented as any one or a combination of general or special-purpose processors (e.g. a field-programmable gate array (FPGA), firmware, software to provide instrument control and data analysis for mass spectrometers and/or related instruments. A sample containing one or more analytes of interest can be ionized via an ion source 52 operating at or near atmospheric or sub-ambient pressure. The resultant ions are directed via predetermined ion optics that often can include tube lenses, skimmers, ion funnels 51, and multipoles (e.g., reference characters 53 and 54) so as to be urged through a series of chambers, e.g., chambers 2, 3 and 4, of progressively reduced pressure that operationally guide and focus such ions to provide good transmission efficiencies. The various chambers communicate with corresponding ports 80 (represented as arrows in FIG. 1A) that are coupled to a set of vacuum pumps (differential pumping, not shown) to maintain the pressures at the desired values.
The example mass spectrometer system 1 of FIG. 1A is shown illustrated to include a triple stage configuration 64 within a high vacuum chamber 5, the triple stage configuration having sections labeled Q1, Q2 and Q3 electrically coupled to respective power supplies (not shown). The Q1, Q2 and Q3 stages may be operated, respectively, as a first quadrupole mass filter, a fragmentation cell, and a second quadrupole mass filter. Ions are analyzed or filtered at the first stage, fragmented at the second stage, and/or analyzed or filtered within the last stage, and are then passed to a detector 66. Such a detector is beneficially placed at the channel exit of the quadrupole (e.g., Q3 of FIG. 1A) to provide ion abundance information that can be processed into a rich mass spectrum (data) 68 showing the variation of ion abundance with respect to m/z ratio. With the recent development of imaging ion detectors for detecting ions emerging from a quadrupole mass filter (see detailed discussion below), three-dimensional information (e.g., two spatial dimensions and one temporal dimension) may be obtained which maintains high mass resolving power without significant degradation of signal intensity.
During conventional operation of a multipole mass filter, such as the quadrupole mass filter Q3 shown in FIG. 1A, to generate a mass spectrum, a detector (e.g., the detector 66 of FIG. 1A) is used to measure the quantity of ions that pass completely through the mass filter as a function of time during the application of superimposed oscillatory radio frequency (RF) and non-oscillatory (DC) electric fields. Thus, at any point in time, the detector only receives those ions having m/z ratios within the mass filter pass band at that time—that is, only those ions having stable trajectories within the multipole under the particular RF and DC voltages that are applied to the quadrupole at that time. Such conventional operation creates a trade-off between instrument resolution and sensitivity. High mass resolving can be achieved, but only if the DC/RF ratio is such that the filter pass band is very narrow, such that most ions develop unstable trajectories within the mass filter and few pass through to the detector. Under such conditions, scans must be performed relatively slowly so as to detect an adequate number of ions at each m/z data point. Conversely, high sensitivity or high speed can also be achieved during conventional operation, but only by widening the pass band, thus causing degradation of m/z resolution.
U.S. Pat. No. 8,389,929, which is assigned to the assignee of the present invention and which is incorporated by reference herein in its entirety, teaches a quadrupole mass filter method and system that discriminates among ion species, even when both are simultaneously stable, by recording where the ions strike a position-sensitive detector as a function of the applied RF and DC fields. When the arrival times and positions are recorded, the resulting data can be thought of as a series of ion images. Each observed ion image is essentially the superposition of component images, one for each distinct m/z value exiting the quadrupole at a given time instant. The same patent also teaches methods for the prediction of an arbitrary ion image as a function of in/z and the applied field. Thus, each individual component image can be extracted from a sequence of observed ion images by mathematical deconvolution or decomposition processes, as further discussed in the aforementioned patent. The mass-to-charge ratio and abundance of each species necessarily follow directly from the deconvolution or decomposition. Accordingly, high mass resolving power can be achieved under a wide variety of operating conditions, a property not usually associated with quadrupole mass spectrometers.
The inventors of U.S. Pat. No. 8,389,929 recognized that ions of different mtz ratios exiting a quadrupole mass filter may be discriminated, even when both ions are simultaneously stable (that is, have stable trajectories) within the mass filter by recording where the ions strike a position-sensitive detector as a function of the applied RF and DC fields. The inventors of U.S. Pat. No. 8,389,929 recognized that such operation is advantageous because when a quadrupole is operated in, for example, a mass filter mode, the scanning of the device that is provided by ramped RF and DC voltages naturally varies the spatial characteristics with time as observed at the exit aperture of the quadrupole. Specifically, ions manipulated by a quadrupole are induced to perform a complex 2-dimensional oscillatory motion on the detector cross section as the scan passes through the stability region of the ions. All ion species of respective m/z ratios express exactly the same motion, across the same range of Mathieu parameter “a” and “q” values (see FIG. 13), but at different respective RF and DC voltages and at different respective times. The ion motion (i.e., for a cloud of ions of the same mtz but with various initial displacements and velocities) may be characterized by the variation of a and q, this variation influencing the position and shape cloud of ions exiting the quadrupole as a function of time. For two masses that are almost identical, the sequence of their respective oscillatory motions is essentially the same and can be approximately related by a time shift.
The teachings of the aforementioned U.S. Pat. No. 8,389,929 exploit the varying spatial characteristics by collecting the spatially dispersed ions of different m/z even as they exit the quadrupole at essentially the same time. FIG. 1B shows a simulated recorded image of a particular pattern at a particular instant in time. The example image can be collected by a fast detector, (i.e., a detector capable of fast sampling within 10 or more RF cycles, more often down to an RF cycle or with sub RF cycles specificity, where said sub-RF specificity is possibly averaged for multiple RF cycles), positioned to acquire where and when ions exit to distinguish fine detail. The motion of ions may be referenced to a conventional Mathieu diagram (FIG. 13). During a mass scan, the (q, a) position of any ion is described by motion along scan line 411. During a scan, the (q, a) position of an ion first approaches (point 413), then enters (point 412), then traverses across (point 415) and finally exits (point 414) the “X & Y stable” portion of the Mathieu diagram. During this time, the y-component of the ion's trajectory changes from “unstable” to “marginally stable” at the instability boundary (point 412) and then becomes increasingly “stable” thereafter (points 415, 414 and 416). Simultaneously, the x-component of the ion's trajectory qualitatively changes in the reverse sense. Watching an ion image formed in the exit cross section progress in time, the ion cloud is elongated and undergoes wild oscillations along the y-axis (herein termed “vertical” oscillations) that carry it beyond the top and bottom of a collected image. Gradually, the exit cloud contracts, and the amplitude of the y-component oscillations decreases when the (q, a) scan line is in the stable region of the ions of interest. If the cloud is sufficiently compact upon entering the quadrupole, the entire cloud remains in the image, i.e. 100% transmission efficiency, during the complete oscillation cycle when the ion is well within the stability region.
FIG. 1B graphically illustrates such a result. In particular, the vertical cloud of ions, as enclosed graphically by the ellipse 6 shown in FIG. 1B, correspond to the heavier ions entering the stability field of the quadrupole and accordingly oscillate with an amplitude that brings such heavy ions close to the denoted y-quadrupoles. The cluster of ions enclosed graphically by the ellipse 8 shown in FIG. 1B correspond to lighter ions exiting the stability field of the quadrupole and thus cause such ions to oscillate with an amplitude that brings such lighter ions close to the denoted x-quadrupoles. Within the image lie the additional clusters of ions (shown in FIG. 1B but not specifically highlighted) that have been collected at the same time frame but which have a different exit pattern because of the differences of their Mathieu a and q parameters.
FIG. 1C illustrates one example of an imaging ion detector system, generally designated by the reference numeral 20 as described in the aforementioned U.S. Pat. No. 8,389,929. As shown in FIG. 1C, incoming ions I (shown directionally by way of accompanying arrows) having for example a beam cross section of about 1 mm or less, varying to the quadrupole's inscribed radius as they exit from an ion occupation volume between quadrupole rod electrodes 101, are received by an assembly 102 of microchannel plates (MCPs) 13a, 13b. Such an assembly can include a pair of MCPs (a Chevron or V-stack) or triple (Z-stack) comprising MCPs adjacent to one another with each individual plate having sufficient gain and resolution to enable operating at appropriate bandwidth requirements (e.g., at about 1 MHz up to about 100 MHz) with the combination of plates generating up to about 107 electrons in response to each incident ion.
To illustrate operability by way of an example, the first surface of the MCP assembly 102 can be floated to 10 kV, (i.e., +10 kV when configured for negative ions and −10 kV when configured to receive positive ions), with the second surface floated to +12 kV and −8 kV respectively, as shown in FIG. 1C. Such a plate biasing provides for a 2 kV voltage gradient to provide the gain with a resultant output relative 8 to 12 kV relative to ground. All high voltages portions are under vacuum between about 10−5 mBar (10−3 Pa) and 10−6 mBar (10−4 Pa).
The example biasing arrangement of FIG. 1C thus enables impinging ions I as received from, for example, the exit of a quadrupole, as discussed above, to induce electrons in the front surface of the first MCP 13a for the case of positive ions, that are thereafter directed to travel along individual channels of the first MCP 13a as accelerated by the applied voltages. As known to those skilled in the art, since each channel of the MCP serves as an independent electron multiplier, the input ions I as received on the channel walls produce emission of secondary electrons (denoted as e−). These electrons are then accelerated by the potential gradient across the ends of each individual MCP 13a, 13b of the MCP stack 102 and strike inner surfaces of the channel causing more emission of electrons that are released from the output end of the MCP stack 102. This process substantially enables the preservation of the pattern (image) of the particles incident on the front surface of the MCP. When operated in negative ion mode, negative ions are initially converted to small positive ions that then induce a similar electron cascade as is well known in the art.
The biasing arrangement of the detector system 20 (FIG. 1C) also provides for the electrons multiplied by the MCP stack 102 to be further accelerated in order to strike an optical component, e.g., a phosphor coated fiber optic plate 15 configured behind the MCP stack 102. Such an arrangement converts the signal electrons to a plurality of resultant photons (denoted as p) that are proportional to the amount of received electrons. Alternatively, an optical component, such as, for example, an aluminized phosphor screen can be provided with a biasing arrangement (not shown) such that the resultant electron cloud from the MCP stack 102 can be drawn across a gap by the high voltage onto a phosphor screen where the kinetic energy of the electrons is released as light. The initial assembly is configured with the goal of converting either a positive or negative ion image emanating from the quadrupole exit into a photon image suitable for acquisition by subsequent photon imaging technology.
The photons p emitted by the phosphor coated fiber optic plate or aluminized phosphor screen 15 are captured and then converted to electrons which are then translated into a digital signal by a two-dimensional camera component 25 (FIG. 1C). In the illustrated arrangement, a plate, such as, a photosensitive channel plate 10 assembly (shown with the anode output biased relative to ground) can convert each incoming photon p back into a photoelectron. Each photoelectron generates a cloud of secondary electrons 11 (indicated as c) at the back of the photosensitive channel plate 10, which spreads and impacts as one arrangement, an array of detection anodes 12, such as, but not limited to, an two-dimensional array of resistive structures, a two-dimensional delay line wedge and strip design, as well as a commercial or custom delay-line anode readout. As part of the design, the photosensitive channel plate 10 and the anodes 12 are in a sealed vacuum enclosure (not shown).
Each of the anodes of the two-dimensional camera 25 shown in FIG. 1C can be coupled to an independent amplifier 14 and additional analog to digital converter (ADC) 18 as known in the art. For example, such independent amplification can be by way of differential transimpedance amplifiers or avalanche photodiodes (APD) to improve the signal-to-noise ratio and transform detected current into voltage. The signals resultant from amplifiers 14 and ADC 18 and/or charge integrators (not shown) can eventually be directed to a Field Programmable Gate Array (FPGA) 22 via, for example, a serial LVDS (low-voltage differential signaling) high-speed digital interface 21, which is a component designed for low power consumption and high noise immunity for the anticipated data rates. The FPGA 21, when electrically coupled to a computer or other data processing means 26, may be operated as an application-specific hardware accelerator for the required computationally intensive tasks.
FIG. 2 schematically depicts another example of an imaging ion detection system as described in U.S. Pat. No. 9,355,828, which is incorporated herein by reference in its entirety. The imaging ion detection system is shown generally in FIG. 2 as detector system 100. The ions I exiting from an ion occupation region between quadrupole rod electrodes 101 are converted to electrons and the electron current is amplified by microchannel plate assembly or stack 102 comprising one or a plurality of microchannel plates as previously described with reference to FIG. 1C. It is preferable to generate photons, within the system 100, using a substrate plate 109 comprising a single-piece or integral component (such as a plate of glass, mica or plastic) that is coated with a transparent material, such as indium tin oxide, comprising a biasing electrode 106 and further coated with a phosphor material comprising a phosphorescent screen 107. A phosphor-coated plate comprising a bundle of fibers (such as plate 15 employed in the system 20 illustrated in FIG. 1C) may alternatively be employed as the substrate plate 109. Voltages V1 and V2 are applied to electrodes at opposite ends of the MCP stack 102 so as to draw ions I onto the stack and to accelerate generated electrons (denoted as e−) through the stack. A voltage V3 is applied to the transparent electrode 106 to draw the electrons onto the phosphorescent screen 107 at which photons (denoted as p) are generated.
The set of components 27 shown on the right hand side of the substrate plate 109 in FIG. 2 serve to replace the two-dimensional camera 25 that is depicted in FIG. 1C. The replacement components comprise two separate linear (one-dimensional or “1-D”) photo-detector arrays 132a, 132b and associated optics. In operation, the phosphorescent screen 107 radiantly “glows” with a spatially-non-uniform intensity as it is impacted by electrons e− that are generated as a result of impingement of ions I onto the microchannel plate assembly or stack 102. The pattern of this spatially-non-uniform glow at any time corresponds to the spatial distribution of the number of ions emitted from between the quadrupole rods 101 at such time. Lens 112 and cylindrical lens 121a serve to transfer an image of the glowing phosphorescent screen onto a first linear photo-detector array (PDA) 132a. Likewise, lens 112 and cylindrical lens 121b serve to transfer a duplicate image of the glowing phosphorescent screen onto a second linear photo-detector array array 132b. An axis of cylindrical lens 121b is oriented substantially perpendicular to an axis of cylindrical lens 121a. Similarly, the individual light sensitive elements of photo-detector array 132b are aligned along a line that is substantially perpendicular to a second line along which the individual light sensitive elements of linear photo-detector array 132a are aligned. The illustrated difference in shape between the first and second cylindrical lenses 121a, 121b is employed so as to indicate that the second cylindrical lens comprises an orientation that is rotated o that its axis is orthogonal to the first cylindrical lens.
Light comprising photons that are generated by the phosphorescent screen 107 and that pass through the substrate plate 109 is collected and partially collimated into a light beam by a light collection lens 112. The partially collimated light beam is then split into two light-beam portions along two respective pathways by a beam splitter 116. A first such pathway—traversed by a first light beam portion—is indicated in FIG. 2 by arrows 117 and a second such pathway—traversed by the second light beam portion—is indicated by arrows 118. These light beam portions thus transfer two copies of the image information. Each of these light beam portions may then comprise about half the intensity of the original light source. Alternatively, the beam splitter 116 may be configured such that the ratio between the intensities of the transmitted and reflected light beam portions is other than one-to-one (1:1), such as, for example, nine-to-one (9:1), four-to-one (4:1), one-to-four (1:4), one-to-nine (1:9), etc. Such beam splitters are commercially available as either off-the-shelf stock items or can be custom fabricated in almost any desired transmitted-to-reflected ratio. A beam splitter in which the transmitted-to-reflected ratio is other than 1:1 may be employed, for example, to deliver a greater proportion of the light beam intensity to a detector having less sensitivity or to deliver a lesser proportion to a detector which might be easily saturated.
Each of the two light beam portions is focused by a respective one of the cylindrical lenses 121a, 121b so as to project a respective one-dimensional image of the phosphor screen onto a onto a respective one of the linear photo-detector arrays 132a, 132b. Optionally, a reflecting device 123 comprising, such as a flat mirror or a prism, may be employed within one of the beam pathways to cause both beams to be parallel. The deflection of one of the beams by the reflecting device 123 may be used to decrease the size of the system 100 or possibly to facilitate mechanical mounting of the two linear photo-detector arrays 132a, 132b to a common circuit board and drive electronics.
According to the configuration illustrated in FIG. 2, the light beam portion that traverses the pathway indicated by arrow 117 is compressed within the x-dimension (see Cartesian axes on left side of FIG. 2) so as to be focused to a line (i.e., a line parallel to the y-dimension, perpendicular to the plane of the drawing of FIG. 2) that is coincident with the position of the first linear photo-detector array 132a. Similarly, the light beam portion that traverses the pathway indicated by arrow 118 is compressed within the y-dimension so as to be focused to a line that is parallel to the x-dimension and that is coincident with the position of the second linear photo-detector array 132b. The light-sensitive regions of the linear photo-detector arrays 132a, 132b are disposed at the foci of the cylindrical lenses 121a, 121b such that each of the light beam portions is focused to a line on the light sensitive region of the respective linear photo-detector array 132a, 132b. The first and second linear photo-detector arrays 132a, 132b may comprise, without limitation, two line cameras. The first and second linear photo-detector arrays 132a, 132b may be substantially identical to one another. However, the first and second linear photo-detector arrays 132a, 132b are depicted differently in FIG. 2 to indicate that the orientation of the second linear photo-detector array 132b is rotated so as to be orthogonal to the first linear photo-detector array 132b. 
FIG. 3 is a schematic depiction of light receiving face of a general linear photo-detector array 132. The array comprises a plurality of individual, independent light-sensitive elements 133, which may be referred to as “pixels”. In the system 100 illustrated in FIG. 2 (as well as in other system embodiments taught herein), an instance of the array 132 may be optically interfaced to either a cylindrical lens 120a, 120b or a line-focusing composite lens with the linearly disposed plurality of pixels oriented so as to be coincident with a line focus produced by the cylindrical lens or composite lens.
As illustrated in FIG. 2, each linear photo-detector array retains image variation along the dimension parallel to the array and sums (or “bins”) image information orthogonal to the array. Because two mutually orthogonal arrays are employed, image variation parallel to both the x-direction and the y-direction (as defined above for quadrupole apparatuses) is retained. Binning the information is a very useful method of data compression without losing much information. The system configuration depicted in FIG. 2 employs optics to enable the use of two separate, simpler, photo-detector arrays, such as line cameras, to provide the same orthogonal information as the previously-described two-dimensional camera 25 (FIG. 1C).
FIG. 4A is a simplified depiction of a portion of a known time and position imaging ion detector system for a mass spectrometer. As noted above, a stream or flux of ions I that are emitted from an exit aperture 108 of a quadrupole 101 comprising four parallel rods are intercepted by a stack 102 of microchannel plates 13a, 13b. In response to the impingement of the ions, a stream or flux of electrons e− are ejected from the MCP stack. The stream or flux of electrons retains spatial information pertaining to the original flux density of intercepted ions at each position on the MCP stack. These electrons are intercepted by a scintillator substrate plate 109 that is coated with a phosphorescent material 107. Conventionally, the phosphorescent material is a sintered powder of e.g. Ce:YAG (cerium-doped yttrium-aluminum garnet). The ions I are urged towards the MCP stack from the quadrupole 101 under the influence of biasing voltage V1 provided by high-voltage supply 31. Ejected electrons are propelled from the first MCP 13a to the second MCP 13b and then to the scintillator plate 109 under the influence of biasing voltages V2 and V3, the latter of which may be supplied to a thin-film electrode coating 104 on the scintillator. The applied voltages, V1 and V2 provide for a 2 kV voltage gradient to provide the gain between the plates. All high voltages portions are under vacuum. An electronic controller 33, which may be a programmed computer or other integrated circuitry that is programmed by firmware, controls the application of voltages to the MCP and electrode 104 and also controls the application of radio frequency (RF) and other voltages to the rod electrodes of quadrupole 101.
The first two components of the detection system (the MCP and the scintillator material) often age unevenly in a short period of time as a result of being impacted by highly intense ion beams that can be focused at specific spots on the MCP and scintillator surfaces within one or more quadrupole 101 RF cycles under vacuum (e.g., 10−5 to 10−6 torr). For example, FIG. 4B shows a time series of ion images of monoisotopic polytyrosine-1 that was captured by a detector system having the components that are illustrated in FIG. 4A. The abscissa in FIG. 4B represents time and the ordinate represents displacement of images along both the y-axis (profile 202 along the top portion of the graph) and along the x-axis (profile 204 along the bottom portion). The signal intensity is represented by the darkness of the shading. The apparent asymmetric ion trajectories observed in the y-dimension at location 205 are due, in part, to the uneven gain distribution of the detection area. The uneven gain across portions of the MCP and/or phosphor surfaces as a result of rapid ion aging imposes an asymmetric wave profile in the time series of images along the y-dimension, as indicated by envelope 209 in FIG. 4C.
In reality, high gains/potentials on both the MCP and the phosphor are often required in order to achieve the detection of single ion event that is a standard requirement for a commercial quadrupole mass spectrometer instrument. The most severe aging is found to occur at positions on the MCP and scintillator at which the beam focuses. Longevity studies on the MCP and phosphor indicate that significant gain changes at specific spots on these plate surfaces over the course of a single week of ordinary quadrupole mass spectrometer operation. FIG. 4D is a schematic depiction of the zone of impingement 211 of ions or electrons on the surface of either a microchannel plate or a scintillator of an imaging ion detector system such as the systems illustrated in FIG. 1C and FIG. 2. In this discussion, the term “transducer” is used to represent either a microchannel plate or a scintillator plate and is identified in the description of the drawings as transducer 215. In other words, each drawing in which transducer 215 is illustrated may represent either or both of two different objects—a first object in which transducer 215 is a microchannel plate and, possibly, a second object in which transducer 215 is a scintillator plate. In the case in which the transducer is a microchannel plate (MCP), the charged particles are ions; in the case in which the transducer is a scintillator plate, the charged particles are electrons. In either case, the center of the transducer surface is depicted at 213.
The region of ion impingement 211 of the transducer 215 comprises two sub-regions, denoted as sub-region 219a and sub-region 219b. Sub-region 219a is a portion of the region 211 within which the charged particles carry sufficient energy to cause rapid degradation of the response of the transducer for a period of time after the transducer is put into service. Sub-region 219b, which is the remainder of zone of impingement region 211, is a portion of the transducer surface within which a measurable amount of charged particles impact the transducer surface but within which the total energy flux is not so great as to cause significant change in the response of a new transducer over short time periods (e.g., several weeks). Although drawn in FIG. 4D with sharp demarcation lines, the outer boundary of region 211 and the boundary between sub-region 219a and sub-region 219b are in fact gradational. Also, the relative dimensions of the transducer 215 and the regions 219a-219b are schematic and not necessarily drawn to scale.
When the transducer 215 is appropriately aligned near an exit aperture of the rods X1, X2, Y1, Y2 (see FIG. 5A), of a quadrupole mass analyzer, the transducer center 213 coincides with the projection of the central longitudinal axis 210 of the quadrupole onto the surface. Because the central longitudinal axis is the location of a pseudopotential well within the quadrupole, all ions that have stable trajectories oscillate about that axis and pass multiple times through a narrow region about the axis as they move through the quadrupole. Accordingly, the sub-region 219a of an MCP receives the greatest quantity of ions over time and the sub-region 219a of a corresponding scintillator plate receives the greatest quantity of electrons over time because of guiding of the ions by a great potential difference along the central longitudinal axis 210. Thus, the sub-region 219a is herein referred to as the zone of ion focusing and is the zone of greatest signal intensity in an ion image produced by an imaging system of the type depicted in FIG. 1C and FIG. 2. Unfortunately, the image details derived from the sub-region 219a can be biased by the transducer aging over the time because the sub-region 219a has the greatest probability of being impacted by ions or electrons, regardless of m/z value. Conversely, the signal derived from sub-region 219b is less intense than the signal derived from sub-region 219b but nonetheless exhibits greater variability with m/z (see FIG. 1B). Mathematical analysis of a time sequence of images requires information from both of the sub-regions 219a, 219b in order to fully resolve component signals corresponding to different respective ion m/z values.
The data processing of imaging quadrupole mass spectrometer systems such as those depicted in FIG. 1C and FIG. 2 comprises deconvolution steps that decompose the complex overlapping data generated by multiple emergent ion species into individual component images, where each component image relates to a one of those species. The data processing further comprises recognition of the temporal variation of such component images. Such data processing steps, which are sensitive to variations of spatial patterns of emerging ions, require consistent measurements from the detection system. If the sensitivity of the detection system should deviate from its condition during the most recent calibration, then system re-calibration is required to prevent data processing performance degradation or complete failure. A weekly calibration schedule, as suggested by longevity experiments, may not be acceptable for most users. Accordingly, there is a need in the art to expand the effective period of the detector calibration in quadrupole mass spectrometer systems that detect ion spatial patterns.